Joint locking (medicine)
A symptom of inability to fully move a joint.
Joint locking can be a symptom of a joint problem, where a person cannot fully bend or straighten it. The same term also refers to the normal way lower limb joints stay fully extended while standing, requiring little muscle effort.
Clinical symptom
Complaints of locking sensation in the knee joint are divided into true locking and pseudo locking. True locking results from damage to intra-articular structures such as ligaments, a loose body, or a meniscal tear; the knee can be unlocked by rotating the leg. A loose body, also called a joint mouse, may be felt in the suprapatellar region or lateral and medial gutter. Pseudolocking occurs when pain prevents full movement without structural causes, and is relieved by massage or painkillers. Joint locking is a common symptom of osteoarthritis, osteochondritis dissecans, synovial osteochondromatosis, meniscal tear, and anterior cruciate ligament injury.
Locking mechanism
When standing up, the knee locks during the final part of extension. The lateral condyle of the femur fills the available space on the tibia’s lateral condyle, forcing the femur to rotate inward. This makes the lateral femoral condyle serve as a pivot, letting the medial condyle shift backward. The quadriceps and the knee’s ligaments, pulling at an angle, assist this motion, and the ligaments become tight once the joint is locked. To unlock the knee for bending, the popliteus muscle rotates the femur outward. Researchers are also studying locking in the hip and midtarsal joint using cadavers.
More in Symptoms and Signs: Musculoskeletal System
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